问题 解答题

在10件产品中,有3件一等品,4件二等品,3件三等品,从这10件产品中任取3件,求取出的3件产品中一等品件数X的分布列。

答案

解:由于从10件产品中任取3件的结果数为

从10件产品中任取3件其中恰有k件一等品的结果数为

那么从10件产品中任取3件,

其中恰有k件一等品的概率为P(X=k)=,k=0,1,2,3,

所以随机变量X的分布列是

单项选择题
完形填空
通读下面短文,掌握其大意,然后在各题所给的A、B、C三个选项中,选出一个最佳选项。
     A young man was going to spend his holiday in a mountain village. That night he    1    at a small hotel
(旅馆) near the train station.    2    going to bed, he went to the owner of the hotel and said, " Excuse me,
sir. Will you please    3    me up at four forty-five tomorrow morning? I'll take the five o'clock    4   ."
     "Oh, sorry," the owner said in a hurry. " I'm afraid I can't. I won't be able to get up so   5    . "
     The young man was going to return to his room    6    he stopped and asked, " Have you got an alarm
clock (闹钟)? Maybe it can help me."
     "Yes, here you are, young man, " said the owner.
     The young man thanked the owner     7   . But as he looked at the alarm clock closely, it seemed there
was    8     wrong with it.
     "Will it     9    on time? " he asked.
     "Sure! You just give it a good shake ( 摇晃 ) at a quarter    10    five, and it will do! "
( ) 1. A. worked      
( ) 2. A. Before      
( ) 3. A. wash        
( ) 4. A. ship        
( ) 5. A. early      
( ) 6. A. when        
( ) 7. A. angrily    
( ) 8. A. something  
( ) 9. A. shout      
( ) 10. A. past      
B. stayed    
B. After      
B. beat      
B. plane      
B. late      
B. because    
B. happily    
B. nothing    
B. cry        
B. to        
C. studied    
C. While      
C. wake      
C. train      
C. quickly    
C. until      
C. sadly      
C. anything  
C. ring      
C. of